Cool, nitrocellulose base, non-carbon forming propellant



United States The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to the field of ordnance and is more particularly concerned with an improved cool gun propellant composition.

In the development of propellants for use in rapid fire guns, it has been necessary to develop compositions having flame temperatures in the range from 1850 to 2000 K. Compositions having these flame temperatures are desirable in order to prevent excessive erosion in rapid fire automatic weapons while having satisfactory ballistic properties. Prior methods of obtaining propellants with flame temperatures in the aforementioned range involved the addition of coolants such as di-nitrotoluene and ethyl centralite to existing formulations. While such formulations will produce propellants having the desired flame temperatures, they will also form solid carbon when employed in rapid fire guns. Another quite different approach has been made by employing a 12% nitrogen nitrocellulose; however, propellants employing such, while having the :desired flame temperatures, also have the undesirable characteristic of being hygroscopic to an extent which is barely acceptable due to the changes in ballistics which are possible if the powders are exposed to a moist atmosphere.

It is therefore an object of this invention to provide new formulations for use as gun propellants which have satisfactory low hygroscopicity, which will not form solid carbon when used in rapid fire guns, and which have flame temperatures low enough to prevent excessive gun wear.

Another object is to provide the aforementioned advantages in a propellant which is easily processed using conventional techniques and apparatus.

The foregoing objects are accomplished by employing the more common 12.6% nitrogen-nitrocellulose, which is easier to process due to its greater solubility in common solvents. Butyl stearate is incorporated into the composition as a coolant while potassium sulfate is incorporated for the purpose of preventing the formation of carbon. Conventional additives in addition to the ones aforementioned are ethyl centralite and diphenylamine which are used to stabilize nitrocellulose and a lead containing salt which upon initiation of the propellant will decompose to metallic lead and form a bore lubricant as is well known in the art. The composition contains from 85 to 87% of the 12.6% N nitrocellulose and incorporates from 6 to about 9% butyl stearate. About 2% potassium sulfate is incorporated into the composition along with about 1% each of ethyl centralite and basic lead carbonate. Volatiles may run up to about 3% of the weight of the product.

The process for preparing the instant gun propellant follows standard procedures for propellant manufacture. The nitrocellulose is mixed with alcohol and ether to form a colloidal mixture. The nitrocellulose may be colloided by the conventional method of mixing alcohol and ether into the fibers to form a solid colloid. The material is broken up mechanically and the proper atent amounts of other constituents are added to give it a proper ratio of nitrocellulose to the other additives. As is usually done an excess amount of volatiles is added. The mix is then placed in a drying room and maintained at a slightly elevated temperature to vaporize the excess volatiles. Periodically a sample is withdrawn from the mix and the rate of burning is measured. As the percent age of volatiles decreases, the burning rate of the propellant is increased and at a point becomes substantially constant. The burning rate is correlated to the ballistic properties of the propellant so that these properties may be controlled.

The following examples are given by way of illustration and are not to be construed as limiting the invention in any way.

Example Example Example 1 2 3 Lot No. Lot No. Lot No.

1X-3l7 1X-329 1X-331 Nitrocellulose (12.6% N) percent- 86. 7 85. 9 86.0 do 6. 3 8. 6 7.9 do 1. 0 1. 0 1. 0 do 1.0 1.0 1.0 do 2.0 2. 0 2.0 do 3.0 1. 5 1. 5 Flame temperature (calculated) 2,000 1,870 1,949

Hygroscopicity determinations were made for the formulations for Examples I, II, and III. The values obtained were respectively 1.68, 1.61, and 1.61 percent of weight gained in thirteen days for the first and eleven days for the last two when exposed to an atmosphere of relative humidity at 30 C. In contrast to this a similar propellant formulation made with 12% N nitrocellulose is 2.3%. The hygroscopicity test consists of exposing propellant samples to a controlled humidity in a desiccator placed in a constant temperature oven. The sample is removed and weighed after various exposure times and then returned to the oven. The test is discontinued when the weight stops changing.

The compositions of Examples 1, II, and III were tested in a standard laboratory carbon formation test which has been shown to correlate very well with carbon formation in rapid fire gun tests. In the test, small samples of the particular propellant under consideration are placed in a bomb and ignited under one atmosphere of nitrogen. Then the head of the bomb is removed, and the amount of carbon formed thereon is visually observed. Tests show that no carbon was formed with the Examples I, II and III. Other compositions similar to Examples I, II, and III having the same or similar flame temperature, but which did not contain potassium sulfate were subjected to the same tests and it was found that at flame temperatures below 2000 K. carbon was for-med.

The advantages of these formulations over previous ones are that they combine in one formulation the noncarbon forming feature and satisfactory hygroscopicity characteristics for propellants having flame temperatures probably not lower than 2000 K. With the bame temperature no more than 2000 K. the erosion of gun barrels in which these propellants are employed is well within accepted standards. The formulations of the prior art either have one of the other of these faults. Another advantage of these new formulations is that they can be manufactured by conventional single-base solvent extrusion procedures with very little changes in procedure, whereas a 12% nitrogen nitrocellulose cannot be.

Obviously many modifications and variations of the present invention are possible in the light of the above 3. The composition of claim 1 in which the stabilizer is diphenylamine.

4. The composition of claim 1 which contains up to about 1% of a lead-containing salt decomposable by the initiation of the propellant.

References Cited in the file of this patent UNITED STATES PATENTS 1,838,345 Woodridge Dec. 29, 1931 2,771,351 Holmes et al. Nov. 20, 1956 2,982,638 Cooley et a1 May 2, 1961 3,028,274 Winer Apr. 3, 1962 

1. A COOL GUM PROPELLANT FORMULATION COMPRISING BY WEIGHT: ABOUT 85-87% NITROCELLULOSE HAVING ABOUT 12.6% NITROGEN, ABOUT 6-9% BUTYL STEARATE, ABOUT 1% STABILIZER, ABOUT 2% POTASSIUM SULFATE, THE REMAINDER ESSENTIALLY VOLATILES. 